1. Field of the Invention
The present invention relates to a winding switching apparatus for switching windings of an alternating current (AC) three-phase motor to extend the range of speed control.
2. Discussion of the Background
For driving devices for main shafts of machine tools and vehicles which are driven by inverter apparatuses, winding switching methods have been adopted to produce a sufficiently large torque in a low-speed range and allow operation in a high-speed range.
For example, U.S. Pat. No. 6,847,185 B2 (family member: Japanese Unexamined Patent Application Publication No. 2003-111492) describes a winding switching apparatus that includes an AC motor having external terminals for switching windings, an inverter unit configured to supply a variable voltage having a variable frequency to the AC motor, and a winding switching unit having semiconductor switches.